1. Technical Field
The present invention relates to a method for producing a spectacle lens which provides the wearer of this lens with at least two types of vision, including ophthalmic vision and an additional vision.
It also relates to such a spectacle lens.
2. Description of the Related Art
In the context of this description, the expression “ophthalmic vision” should be understood to mean the visible perception of the environment of a subject, such that this environment appears to him in front of him by using, if necessary, correcting or solar lenses. However, such lenses do not modify the information which is contained in the images that are thus perceived.
Unlike the ophthalmic vision, an additional vision may provide the subject with information that does not originate directly from his environment. It may be data presented to the subject. For example, navigation data which are projected overlaid on the visor of an airplane pilot's headset constitute an additional vision, of the informative vision type. An additional vision of another type may supply modified images of certain parts of the subject's environment. Thus, other examples of additional vision are the provision of an infrared image which is converted into visible light, or an image of a part of the subject's environment which is enlarged.
A spectacle lens to which the invention is applied is designed to present such additional images in the field of vision of the wearer, or in a part of this field, while retaining the ophthalmic vision. In other words, the two visions, ophthalmic and additional, are available to the wearer. They may be available simultaneously or alternately. In the case of an informative additional vision, the additional image corresponds to the visual presentation of information data. These data may appear overlaid on the ophthalmic image, notably with a light intensity which is greater or with a color which is distinct. The ophthalmic image may remain visible or not while the data of the informative additional vision are presented to the wearer.
It is known to produce such a spectacle lens which comprises:                a front face and a rear face, the rear face facing toward the eye of the wearer for the position of use of the lens;        a refringent medium, which is situated between these front and rear faces; and        an insert, which is situated within the refringent medium, and which is designed to deliver, between the front and rear faces of the lens, through an output window of the insert toward the eye of the wearer, an additional light forming the additional image visible to the wearer in the position of use of the lens.        
The ophthalmic vision then corresponds to the image which is formed by the light having passed in succession through the front face, a front portion of the refringent medium situated on a front side of the insert, the insert or an intermediate part of the refringent medium situated outside a peripheral edge of the insert, a rear portion of the refringent medium situated on a rear side of the insert, and the rear face of the spectacle lens. The alternation between the insert and the intermediate portion of the refringent medium, for the passage of the light for the ophthalmic vision, occurs when the insert does not occupy all the surface area of the spectacle lens which is available for the ophthalmic vision.
The additional vision corresponds to the additional image which is formed by the additional light, this additional light passing through the insert, the rear portion of the refringent medium and the rear face of the spectacle lens.
FIGS. 1a and 1b illustrate the principle of such a spectacle lens which provides the ophthalmic vision and an additional vision. It comprises a basic lens 1 within which is positioned the insert 2. The basic lens 1 consists of a transparent and refringent material, which may be any organic or mineral material used in the ophthalmic field. The basic lens 1 has a convex front face FA and a concave rear face FP. The faces FA and FP have respective curvatures which together determine, with the value of a light refractive index for the refringent medium of the basic lens 1, an optical power of the spectacle lens outside the insert 2, for the ophthalmic vision. This optical power may vary between the directions in which the wearer looks through the lens which are different.
The insert 2 may be a relatively thin light guide, which is positioned between the faces FA and FP of the basic lens 1. It may have light reflection and/or refringence characteristics which are different from those of the basic lens 1, and which are appropriate for bringing the additional light VS from a source 3 which is not represented in detail. The light VS is thus brought to an insert output window FS which faces the eye of the wearer. The structure of the insert 2 is not the subject of this description, and reference can be made to other documents available on this subject. Generally, the basic lens 1 may have a front portion 1a which is between the insert 2 and the front face FA, and a rear portion 1p which is between the insert 2 and the rear face FP. The insert 2 may also be limited transversely within an area of the basic lens 1, in certain directions approximately parallel to the faces FA and FP. In such a configuration, the front portion 1a and the rear portion 1p of the basic lens 1 extend beyond a peripheral edge 2b of the insert 2. The basic lens 1 then has an intermediate portion 1b which extends beyond the edge 2b of the insert 2, and which continually links the portions 1a and 1b to a peripheral edge B of the basic lens 1. The edge B of the basic lens 1 may, for example, be circular with a diameter of 60 mm (millimeters).
As indicated in FIG. 1b, the angular aperture of the additional vision, denoted Σ, is limited by the output window FS of the insert 2. Its pole is a center O of rotation of the eye 10 of the wearer behind the lens. Typically, the aperture Σ may be +/−15° (degree) either side of an optical axis of the additional vision, which passes through the center of the window FS. The generatrix lines of the limit of the aperture Σ intersect the rear face FP of the lens defining an area Z within this face, in which the two visions, ophthalmic and additional, are superposed. In the configuration of FIGS. 1a and 1b, the respective optical axes of the ophthalmic vision and of the additional vision are one and the same, but they may be distinct.
FIGS. 1a and 1b represent the spectacle lens in the position of use by the wearer. The eye of the wearer, referenced 10, is therefore situated behind the lens, on the side of the rear face FP so that it receives, on the one hand, light VO originating from the environment which is situated in front of the lens, and, on the other hand, the light VS which is brought by the insert 2. The light beams of the two lights VO and VS correspond respectively to the ophthalmic vision and to the additional vision. They respectively form, after having passed through the pupil 11, an ophthalmic image and an additional image on the retina 12 of the wearer. The reference 13 designates the iris of the wearer which surrounds his pupil 11. The direction in which the wearer is looking corresponds to the optical axis of the eye 10. It intersects the faces FA and FP of the spectacle lens at respective points which vary when the eye 10 turns in the orbit of the wearer.
Given that the light VO passes through the two faces FA and FP of the lens, they both contribute to optical characteristics of the lens which are relative to the ophthalmic vision. However, the light VS does not pass through the face FA, so that this face does not contribute to optical characteristics of the lens which are relative to the additional vision. Because of this difference between the lights VO and VS, they do not present convergence characteristics which are identical after they have passed through the rear face FP of the lens. For this reason, the ophthalmic and additional images which are formed on the retina are not simultaneously clear.
The expression “optical characteristics of lens which are relative to one or other of the ophthalmic and additional visions” should be understood notably to mean an optical power value, astigmatism values, optical distortion values, etc., of the lens for each direction in which the wearer looks.
The focusing difference between the additional image and the ophthalmic image on the retina 12 may be compensated by an accommodation of the eye 10 of the wearer. The document WO 2008/003903 introduces an accommodative effort limit for the wearer, when he switches from the ophthalmic vision to the additional vision. This limit of the accommodative effort depends in particular on the age of the wearer. However, the two ophthalmic and additional images nevertheless retain optical aberrations, notably when the direction of look varies through the spectacle lens and/or through the output window FS of the insert 2. In the context of the present invention, the expression “optical aberrations” should be understood to mean variations of optical power or astigmatism relative to prescribed values, or any other higher order aberration which may be characterized, notably, by the Zernike polynomials.
FIGS. 2a-2d and 3a-3d relate to spectacle lenses with two ophthalmic and additional visions, which are produced without implementing the present invention.
FIGS. 2a and 2b are respective maps of average optical power and astigmatism for a first spectacle lens, which illustrate these aberrations for the ophthalmic vision. This first lens corresponds to a myopia correction prescription of −4.00 dioptries, without astigmatism correction. The index of the refringent material of the basic lens 1 is 1.60. Each map indicates the values of the average optical power or of the astigmatism of the spectacle lens, when the direction of look varies through the lens. The x and y axes identify the angles α and β between the direction of look and a reference direction, respectively in a vertical plane and in a horizontal plane. The reference direction which is considered passes through a reference point of the spectacle lens. This reference point may notably be the mounting cross which is used to position the lens in a spectacle frame housing. Each curve in these maps links directions of look which correspond to one and the same average optical power or astigmatism value, indicated in dioptries on the curve concerned. As FIG. 2a shows, a negative average optical power difference, which reaches −1.25 dioptries, appears at the periphery of the lens for the ophthalmic vision, relative to the prescribed value produced for the reference direction (α=β=0). This difference is due to a curvature of the front face FA of the lens which is unsuited to the optical aberrations, because this curvature has been reduced to limit the accommodative effort of the wearer in additional vision mode. For the same reason, the map of FIG. 2b shows that the astigmatism increases strongly when the direction of look deviates from the reference direction, toward the periphery of the lens.
FIGS. 2c and 2d are maps of average optical power and astigmatism, which have been established again for the same first spectacle lens but for the additional vision. FIG. 2c shows in particular that the accommodative effort which has been selected is approximately −1.00 dioptry, according to the value of the average optical power for the reference direction.
In the case of such a spectacle lens for a myopic wearer, the average optical power difference is negative for the two visions (FIGS. 2a and 2c), in the peripheral area of the lens relative to the reference direction. It can therefore be compensated if necessary by an accommodation of the eye of the wearer, when he looks obliquely through the lens.
FIGS. 3a to 3d respectively correspond to FIGS. 2a to 2d for a second lens with two visions, which corresponds to a hypermetropia prescription of +2.00 dioptries, −2.00 dioptries and 135°, expressed as cylinder values according to the negative convention. The average optical power for the reference direction (α=β=0) is then approximately +1.00 dioptry (FIG. 3a). For such a hypermetropia correction, the inadequate curvature of the front face FA of the lens provokes a difference between the average optical power of the lens in the peripheral area and the value for the reference correction which is positive for the ophthalmic vision. It therefore opposes the accommodation faculty of the eye, and the resulting ophthalmic constraint is then very significant. Moreover, the accommodative effort of this second lens for the additional vision is approximately −2.25 dioptries (FIGS. 3a and 3c).
FIGS. 2a to 2d and 3a to 3d therefore show that the optical aberrations of the two lens reduce the field of the ophthalmic vision and that of the additional vision in both horizontal and vertical planes. This reduction is particularly detrimental for the ophthalmic vision, notably when the dimensions of the housing of the lens in the spectacle frame are great. The reduction of the field of the additional vision also prevents the use of inserts with wide output window.